// Copyright 2013 The Flutter Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'dart:js_interop';

import 'package:meta/meta.dart';
import 'package:ui/ui.dart' as ui;
import 'package:ui/ui_web/src/ui_web.dart' as ui_web;
import 'package:web_locale_keymap/web_locale_keymap.dart' as locale_keymap;

import 'dom.dart';
import 'initialization.dart';
import 'key_map.g.dart';
import 'platform_dispatcher.dart';
import 'raw_keyboard.dart';
import 'renderer.dart';
import 'semantics.dart';

typedef _VoidCallback = void Function();
typedef ValueGetter<T> = T Function();
typedef _ModifierGetter = bool Function(FlutterHtmlKeyboardEvent event);

// Set this flag to true to see all the fired events in the console.
const bool _debugLogKeyEvents = false;

const int _kLocationLeft = 1;
const int _kLocationRight = 2;

final int _kLogicalAltLeft = kWebLogicalLocationMap['Alt']![_kLocationLeft]!;
final int _kLogicalAltRight = kWebLogicalLocationMap['Alt']![_kLocationRight]!;
final int _kLogicalControlLeft = kWebLogicalLocationMap['Control']![_kLocationLeft]!;
final int _kLogicalControlRight = kWebLogicalLocationMap['Control']![_kLocationRight]!;
final int _kLogicalShiftLeft = kWebLogicalLocationMap['Shift']![_kLocationLeft]!;
final int _kLogicalShiftRight = kWebLogicalLocationMap['Shift']![_kLocationRight]!;
final int _kLogicalMetaLeft = kWebLogicalLocationMap['Meta']![_kLocationLeft]!;
final int _kLogicalMetaRight = kWebLogicalLocationMap['Meta']![_kLocationRight]!;

final int _kPhysicalAltLeft = kWebToPhysicalKey['AltLeft']!;
final int _kPhysicalAltRight = kWebToPhysicalKey['AltRight']!;
final int kPhysicalControlLeft = kWebToPhysicalKey['ControlLeft']!;
final int kPhysicalControlRight = kWebToPhysicalKey['ControlRight']!;
final int _kPhysicalShiftLeft = kWebToPhysicalKey['ShiftLeft']!;
final int _kPhysicalShiftRight = kWebToPhysicalKey['ShiftRight']!;
final int _kPhysicalMetaLeft = kWebToPhysicalKey['MetaLeft']!;
final int _kPhysicalMetaRight = kWebToPhysicalKey['MetaRight']!;

// Map logical keys for modifier keys to the functions that can get their
// modifier flag out of an event.
final Map<int, _ModifierGetter> _kLogicalKeyToModifierGetter = <int, _ModifierGetter>{
  _kLogicalAltLeft: (FlutterHtmlKeyboardEvent event) => event.altKey,
  _kLogicalAltRight: (FlutterHtmlKeyboardEvent event) => event.altKey,
  _kLogicalControlLeft: (FlutterHtmlKeyboardEvent event) => event.ctrlKey,
  _kLogicalControlRight: (FlutterHtmlKeyboardEvent event) => event.ctrlKey,
  _kLogicalShiftLeft: (FlutterHtmlKeyboardEvent event) => event.shiftKey,
  _kLogicalShiftRight: (FlutterHtmlKeyboardEvent event) => event.shiftKey,
  _kLogicalMetaLeft: (FlutterHtmlKeyboardEvent event) => event.metaKey,
  _kLogicalMetaRight: (FlutterHtmlKeyboardEvent event) => event.metaKey,
};

const String _kPhysicalCapsLock = 'CapsLock';

const String _kLogicalDead = 'Dead';

const int _kWebKeyIdPlane = 0x1700000000;

// Bits in a Flutter logical event to generate the logical key for dead keys.
//
// Logical keys for dead keys are generated by annotating physical keys with
// modifiers (see `_getLogicalCode`).
const int _kDeadKeyCtrl = 0x10000000;
const int _kDeadKeyShift = 0x20000000;
const int _kDeadKeyAlt = 0x40000000;
const int _kDeadKeyMeta = 0x80000000;

const ui.KeyData _emptyKeyData = ui.KeyData(
  type: ui.KeyEventType.down,
  timeStamp: Duration.zero,
  logical: 0,
  physical: 0,
  character: null,
  synthesized: false,
);

typedef DispatchKeyData = bool Function(ui.KeyData data);

/// Converts a floating number timestamp (in milliseconds) to a [Duration] by
/// splitting it into two integer components: milliseconds + microseconds.
Duration _eventTimeStampToDuration(num milliseconds) {
  final int ms = milliseconds.toInt();
  final int micro = ((milliseconds - ms) * Duration.microsecondsPerMillisecond).toInt();
  return Duration(milliseconds: ms, microseconds: micro);
}

// Returns a function that caches the result of `body`, ensuring that `body` is
// only run once.
ValueGetter<T> _cached<T>(ValueGetter<T> body) {
  T? cache;
  return () {
    return cache ??= body();
  };
}

class KeyboardBinding {
  KeyboardBinding._() {
    _addEventListener('keydown', (DomEvent domEvent) {
      final FlutterHtmlKeyboardEvent event = FlutterHtmlKeyboardEvent(domEvent as DomKeyboardEvent);
      _converter.handleEvent(event);
      RawKeyboard.instance?.handleHtmlEvent(domEvent);
    });
    _addEventListener('keyup', (DomEvent domEvent) {
      final FlutterHtmlKeyboardEvent event = FlutterHtmlKeyboardEvent(domEvent as DomKeyboardEvent);
      _converter.handleEvent(event);
      RawKeyboard.instance?.handleHtmlEvent(domEvent);
    });
  }

  /// The singleton instance of this object.
  static KeyboardBinding? get instance => _instance;
  static KeyboardBinding? _instance;

  static void initInstance() {
    if (_instance == null) {
      _instance = KeyboardBinding._();
      assert(() {
        registerHotRestartListener(_instance!._reset);
        return true;
      }());
    }
  }

  /// The platform as used in the initialization.
  ///
  /// By default it is derived from [operatingSystem].
  @protected
  ui_web.OperatingSystem get localPlatform {
    return ui_web.browser.operatingSystem;
  }

  KeyboardConverter get converter => _converter;
  late final KeyboardConverter _converter = KeyboardConverter(_onKeyData, localPlatform);
  final Map<String, DomEventListener> _listeners = <String, DomEventListener>{};

  void _addEventListener(String eventName, DartDomEventListener handler) {
    void loggedHandler(DomEvent event) {
      if (_debugLogKeyEvents) {
        print(event.type);
      }
      if (EngineSemantics.instance.receiveGlobalEvent(event)) {
        handler(event);
      }
    }

    final DomEventListener wrappedHandler = loggedHandler.toJS;
    assert(!_listeners.containsKey(eventName));
    _listeners[eventName] = wrappedHandler;
    domWindow.addEventListener(eventName, wrappedHandler, true.toJS);
  }

  /// Remove all active event listeners.
  void _clearListeners() {
    _listeners.forEach((String eventName, DomEventListener listener) {
      domWindow.removeEventListener(eventName, listener, true.toJS);
    });
    _listeners.clear();
  }

  bool _onKeyData(ui.KeyData data) {
    bool? result;
    // This callback is designed to be invoked synchronously. This is enforced
    // by `result`, which starts null and is asserted non-null when returned.
    EnginePlatformDispatcher.instance.invokeOnKeyData(data, (bool handled) {
      result = handled;
    });
    return result!;
  }

  void _reset() {
    _clearListeners();
    _converter.dispose();
  }
}

class AsyncKeyboardDispatching {
  AsyncKeyboardDispatching({required this.keyData, this.callback});

  final ui.KeyData keyData;
  final _VoidCallback? callback;
}

// A wrapper of [DomKeyboardEvent] with reduced methods delegated to the event
// for the convenience of testing.
class FlutterHtmlKeyboardEvent {
  FlutterHtmlKeyboardEvent(this._event);

  final DomKeyboardEvent _event;

  String get type => _event.type;
  String? get code => _event.code;
  String? get key => _event.key;
  int get keyCode => _event.keyCode.toInt();
  bool? get repeat => _event.repeat;
  int? get location => _event.location.toInt();
  num? get timeStamp => _event.timeStamp;
  bool get altKey => _event.altKey;
  bool get ctrlKey => _event.ctrlKey;
  bool get shiftKey => _event.shiftKey ?? false;
  bool get metaKey => _event.metaKey;
  bool get isComposing => _event.isComposing;

  bool getModifierState(String key) => _event.getModifierState(key);
  void preventDefault() => _event.preventDefault();
  void stopPropagation() => _event.stopPropagation();
  bool get defaultPrevented => _event.defaultPrevented;
}

// Reads [DomKeyboardEvent], then [dispatches ui.KeyData] accordingly.
//
// The events are read through [handleEvent], and dispatched through the
// [dispatchKeyData] as given in the constructor. Some key data might be
// dispatched asynchronously.
class KeyboardConverter {
  KeyboardConverter(this.performDispatchKeyData, ui_web.OperatingSystem platform)
    : onDarwin = platform == ui_web.OperatingSystem.macOs || platform == ui_web.OperatingSystem.iOs,
      _mapping = _mappingFromPlatform(platform);

  final DispatchKeyData performDispatchKeyData;

  /// Whether the current platform is macOS or iOS, which affects how certain key
  /// events are comprehended, including CapsLock and key guarding.
  final bool onDarwin;

  /// Maps logical keys from key event properties.
  final locale_keymap.LocaleKeymap _mapping;

  static locale_keymap.LocaleKeymap _mappingFromPlatform(ui_web.OperatingSystem platform) {
    return switch (platform) {
      ui_web.OperatingSystem.iOs ||
      ui_web.OperatingSystem.macOs => locale_keymap.LocaleKeymap.darwin(),
      ui_web.OperatingSystem.windows => locale_keymap.LocaleKeymap.win(),
      ui_web.OperatingSystem.android ||
      ui_web.OperatingSystem.linux ||
      ui_web.OperatingSystem.unknown => locale_keymap.LocaleKeymap.linux(),
    };
  }

  // The `performDispatchKeyData` wrapped with tracking logic.
  //
  // It is non-null only during `handleEvent`. All events during `handleEvent`
  // should be dispatched with `_dispatchKeyData`, others with
  // `performDispatchKeyData`.
  DispatchKeyData? _dispatchKeyData;

  bool _disposed = false;
  void dispose() {
    _disposed = true;
    clearPressedKeys();
  }

  // On macOS, CapsLock behaves differently in that, a keydown event occurs when
  // the key is pressed and the light turns on, while a keyup event occurs when the
  // key is pressed and the light turns off. Flutter considers both events as
  // key down, and synthesizes immediate cancel events following them. The state
  // of "whether CapsLock is on" should be accessed by "activeLocks".
  bool _shouldSynthesizeCapsLockUp() {
    return onDarwin;
  }

  // ## About Key guards
  //
  // When the user enters a browser/system shortcut (e.g. `Cmd+Alt+i`) the
  // browser doesn't send a keyup for it. This puts the framework in a corrupt
  // state because it thinks the key was never released.
  //
  // To avoid this, we rely on the fact that browsers send repeat events
  // while the key is held down by the user. If we don't receive a repeat
  // event within a specific duration (_kKeydownCancelDurationMac) we assume
  // the user has released the key and we synthesize a keyup event.
  bool _shouldDoKeyGuard() {
    return onDarwin;
  }

  /// After a keydown is received, this is the duration we wait for a repeat event
  /// before we decide to synthesize a keyup event.
  ///
  /// This value is only for macOS, where the keyboard repeat delay goes up to
  /// 2000ms.
  static const Duration _kKeydownCancelDurationMac = Duration(milliseconds: 2000);

  static int _getPhysicalCode(String code) {
    if (code.isEmpty) {
      return _kWebKeyIdPlane;
    }
    return kWebToPhysicalKey[code] ?? (code.hashCode + _kWebKeyIdPlane);
  }

  static int _getModifierMask(FlutterHtmlKeyboardEvent event) {
    final bool altDown = event.altKey;
    final bool ctrlDown = event.ctrlKey;
    final bool shiftDown = event.shiftKey;
    final bool metaDown = event.metaKey;
    return (altDown ? _kDeadKeyAlt : 0) +
        (ctrlDown ? _kDeadKeyCtrl : 0) +
        (shiftDown ? _kDeadKeyShift : 0) +
        (metaDown ? _kDeadKeyMeta : 0);
  }

  // Whether `event.key` is a key name, such as "Shift", or otherwise a
  // character, such as "S" or "ж".
  //
  // A key name always has more than 1 code unit, and they are all alnums.
  // Character keys, however, can also have more than 1 code unit: en-in
  // maps KeyL to L̥/l̥. To resolve this, we check the second code unit.
  static bool _eventKeyIsKeyName(String key) {
    return key.length > 1 && key.codeUnitAt(0) < 0x7F && key.codeUnitAt(1) < 0x7F;
  }

  static int _deadKeyToLogicalKey(int physicalKey, FlutterHtmlKeyboardEvent event) {
    // 'Dead' is used to represent dead keys, such as a diacritic to the
    // following base letter (such as Option-e results in ´).
    //
    // Assume they can be told apart with the physical key and the modifiers
    // pressed.
    return physicalKey + _getModifierMask(event) + _kWebKeyIdPlane;
  }

  // Map from pressed physical key to corresponding pressed logical key.
  //
  // Multiple physical keys can be mapped to the same logical key, usually due
  // to positioned keys (left/right/numpad) or multiple keyboards.
  final Map<int, int> _pressingRecords = <int, int>{};

  // Schedule the dispatching of an event in the future. The `callback` will
  // invoked before that.
  //
  // Returns a callback that cancels the schedule. Disposal of
  // `KeyBoardConverter` also cancels the shedule automatically.
  _VoidCallback _scheduleAsyncEvent(
    Duration duration,
    ValueGetter<ui.KeyData> getData,
    _VoidCallback callback,
  ) {
    bool canceled = false;
    Future<void>.delayed(duration).then<void>((_) {
      if (!canceled && !_disposed) {
        callback();
        // This dispatch is performed asynchronously, therefore should not use
        // `_dispatchKeyData`.
        performDispatchKeyData(getData());
      }
    });
    return () {
      canceled = true;
    };
  }

  final Map<int, _VoidCallback> _keyGuards = <int, _VoidCallback>{};
  // Call this method on the down or repeated event of a non-modifier key.
  void _startGuardingKey(int physicalKey, int logicalKey, Duration currentTimeStamp) {
    if (!_shouldDoKeyGuard()) {
      return;
    }
    final _VoidCallback cancelingCallback = _scheduleAsyncEvent(
      _kKeydownCancelDurationMac,
      () => ui.KeyData(
        timeStamp: currentTimeStamp + _kKeydownCancelDurationMac,
        type: ui.KeyEventType.up,
        physical: physicalKey,
        logical: logicalKey,
        character: null,
        synthesized: true,
      ),
      () {
        _pressingRecords.remove(physicalKey);
      },
    );
    _keyGuards.remove(physicalKey)?.call();
    _keyGuards[physicalKey] = cancelingCallback;
  }

  // Call this method on an up event of a non-modifier key.
  void _stopGuardingKey(int physicalKey) {
    _keyGuards.remove(physicalKey)?.call();
  }

  void _handleEvent(FlutterHtmlKeyboardEvent event) {
    final Duration timeStamp = _eventTimeStampToDuration(event.timeStamp!);

    final String eventKey = event.key!;

    final int physicalKey = _getPhysicalCode(event.code!);
    final bool logicalKeyIsCharacter = !_eventKeyIsKeyName(eventKey);
    // The function body might or might not be evaluated. If the event is a key
    // up event, the resulting event will simply use the currently pressed
    // logical key.
    final ValueGetter<int> logicalKey = _cached<int>(() {
      // Mapped logical keys, such as ArrowLeft, Escape, AudioVolumeDown.
      final int? mappedLogicalKey = kWebToLogicalKey[eventKey];
      if (mappedLogicalKey != null) {
        return mappedLogicalKey;
      }
      // Keys with locations, such as modifier keys (Shift) or numpad keys.
      if (kWebLogicalLocationMap.containsKey(event.key)) {
        final int? result = kWebLogicalLocationMap[event.key!]?[event.location!];
        assert(result != null, 'Invalid modifier location: ${event.key}, ${event.location}');
        return result!;
      }
      // Locale-sensitive keys: letters, digits, and certain symbols.
      if (logicalKeyIsCharacter) {
        final int? localeLogicalKeys = _mapping.getLogicalKey(event.code, event.key, event.keyCode);
        if (localeLogicalKeys != null) {
          return localeLogicalKeys;
        }
      }
      // Dead keys that are not handled by the locale mapping.
      if (eventKey == _kLogicalDead) {
        return _deadKeyToLogicalKey(physicalKey, event);
      }
      // Minted logical keys.
      return eventKey.hashCode + _kWebKeyIdPlane;
    });

    assert(event.type == 'keydown' || event.type == 'keyup');
    final bool isPhysicalDown =
        event.type == 'keydown' ||
        // On macOS, both keydown and keyup events of CapsLock should be considered keydown,
        // followed by an immediate cancel event.
        (_shouldSynthesizeCapsLockUp() && event.code! == _kPhysicalCapsLock);

    final ui.KeyEventType type;

    if (_shouldSynthesizeCapsLockUp() && event.code! == _kPhysicalCapsLock) {
      // Case 1: Handle CapsLock on macOS
      //
      // On macOS, both keydown and keyup events of CapsLock are considered
      // keydown, followed by an immediate synchronized up event.

      _scheduleAsyncEvent(
        Duration.zero,
        () => ui.KeyData(
          timeStamp: timeStamp,
          type: ui.KeyEventType.up,
          physical: physicalKey,
          logical: logicalKey(),
          character: null,
          synthesized: true,
        ),
        () {
          _pressingRecords.remove(physicalKey);
        },
      );
      type = ui.KeyEventType.down;
    } else if (isPhysicalDown) {
      // Case 2: Handle key down of normal keys
      if (_pressingRecords[physicalKey] != null) {
        // This physical key is being pressed according to the record.
        if (event.repeat ?? false) {
          // A normal repeated key.
          type = ui.KeyEventType.repeat;
        } else {
          // A non-repeated key has been pressed that has the exact physical key as
          // a currently pressed one. This can mean one of the following cases:
          //
          //  * Multiple keyboards are pressing keys with the same physical key.
          //  * The up event was lost during a loss of focus.
          //  * The previous down event was a system shortcut and its release
          //    was skipped (see `_startGuardingKey`,) such as holding Ctrl and
          //    pressing V then V, within the "guard window".
          //
          // The three cases can't be distinguished, and in the 3rd case, the
          // latter event must be dispatched as down events for the framework to
          // correctly recognize and choose to not to handle. Therefore, an up
          // event is synthesized before it.
          _dispatchKeyData!(
            ui.KeyData(
              timeStamp: timeStamp,
              type: ui.KeyEventType.up,
              physical: physicalKey,
              logical: _pressingRecords[physicalKey]!,
              character: null,
              synthesized: true,
            ),
          );
          _pressingRecords.remove(physicalKey);
          type = ui.KeyEventType.down;
        }
      } else {
        // This physical key is not being pressed according to the record. It's a
        // normal down event, whether the system event is a repeat or not.
        type = ui.KeyEventType.down;
      }
    } else {
      // isPhysicalDown is false and not CapsLock
      // Case 2: Handle key up of normal keys
      if (_pressingRecords[physicalKey] == null) {
        // The physical key has been released before. It indicates multiple
        // keyboards pressed keys with the same physical key. Ignore the up event.
        event.preventDefault();
        return;
      }

      type = ui.KeyEventType.up;
    }

    // The _pressingRecords[physicalKey] might have been changed during the last
    // `if` clause.
    final int? lastLogicalRecord = _pressingRecords[physicalKey];

    final int? nextLogicalRecord;
    switch (type) {
      case ui.KeyEventType.down:
        assert(lastLogicalRecord == null);
        nextLogicalRecord = logicalKey();
      case ui.KeyEventType.up:
        assert(lastLogicalRecord != null);
        nextLogicalRecord = null;
      case ui.KeyEventType.repeat:
        assert(lastLogicalRecord != null);
        nextLogicalRecord = lastLogicalRecord;
    }
    if (nextLogicalRecord == null) {
      _pressingRecords.remove(physicalKey);
    } else {
      _pressingRecords[physicalKey] = nextLogicalRecord;
    }

    // After updating _pressingRecords, synchronize modifier states. The
    // `event.***Key` fields can be used to reduce some omitted modifier key
    // events. We can synthesize key up events if they are false. Key down
    // events can not be synthesized since we don't know which physical key they
    // represent.
    _kLogicalKeyToModifierGetter.forEach((int testeeLogicalKey, _ModifierGetter getModifier) {
      // Do not synthesize for the key of the current event. The event is the
      // ground truth.
      if (logicalKey() == testeeLogicalKey) {
        return;
      }
      if (_pressingRecords.containsValue(testeeLogicalKey) && !getModifier(event)) {
        _pressingRecords.removeWhere((int physicalKey, int logicalRecord) {
          if (logicalRecord != testeeLogicalKey) {
            return false;
          }

          _dispatchKeyData!(
            ui.KeyData(
              timeStamp: timeStamp,
              type: ui.KeyEventType.up,
              physical: physicalKey,
              logical: testeeLogicalKey,
              character: null,
              synthesized: true,
            ),
          );

          return true;
        });
      }
    });

    // Update key guards
    if (logicalKeyIsCharacter) {
      if (nextLogicalRecord != null) {
        _startGuardingKey(physicalKey, logicalKey(), timeStamp);
      } else {
        _stopGuardingKey(physicalKey);
      }
    }

    final String? character = logicalKeyIsCharacter ? eventKey : null;
    final ui.KeyData keyData = ui.KeyData(
      timeStamp: timeStamp,
      type: type,
      physical: physicalKey,
      logical: lastLogicalRecord ?? logicalKey(),
      character: type == ui.KeyEventType.up ? null : character,
      synthesized: false,
    );

    final bool primaryHandled = _dispatchKeyData!(keyData);
    if (primaryHandled) {
      event.preventDefault();
    }
  }

  // Parse the HTML event, update states, and dispatch Flutter key data through
  // [performDispatchKeyData].
  //
  //  * The method might dispatch some synthesized key data first to update states,
  //    results discarded.
  //  * Then it dispatches exactly one non-synthesized key data that corresponds
  //    to the `event`, i.e. the primary key data. If this dispatching returns
  //    true, then this event will be invoked `preventDefault`.
  //  * Some key data might be synthesized to update states after the main key
  //    data. They are always scheduled asynchronously with results discarded.
  void handleEvent(FlutterHtmlKeyboardEvent event) {
    // Autofill on Chrome sends keyboard events whose key and code are null.
    if (event.key == null || event.code == null) {
      return;
    }

    if (kDebugMode &&
        event.key == 'F10' &&
        event.altKey &&
        event.type == 'keydown' &&
        !(event.repeat ?? false)) {
      renderer.dumpDebugInfo();
    }

    assert(_dispatchKeyData == null);
    bool sentAnyEvents = false;
    _dispatchKeyData = (ui.KeyData data) {
      sentAnyEvents = true;
      return performDispatchKeyData(data);
    };
    try {
      _handleEvent(event);
    } finally {
      if (!sentAnyEvents) {
        _dispatchKeyData!(_emptyKeyData);
      }
      _dispatchKeyData = null;
    }
  }

  // Synthesize modifier keys up or down events only when the known pressing states are different.
  void synthesizeModifiersIfNeeded(
    bool altPressed,
    bool controlPressed,
    bool metaPressed,
    bool shiftPressed,
    num eventTimestamp,
  ) {
    _synthesizeModifierIfNeeded(
      _kPhysicalAltLeft,
      _kPhysicalAltRight,
      _kLogicalAltLeft,
      altPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
      eventTimestamp,
    );
    _synthesizeModifierIfNeeded(
      kPhysicalControlLeft,
      kPhysicalControlRight,
      _kLogicalControlLeft,
      controlPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
      eventTimestamp,
    );
    _synthesizeModifierIfNeeded(
      _kPhysicalMetaLeft,
      _kPhysicalMetaRight,
      _kLogicalMetaLeft,
      metaPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
      eventTimestamp,
    );
    _synthesizeModifierIfNeeded(
      _kPhysicalShiftLeft,
      _kPhysicalShiftRight,
      _kLogicalShiftLeft,
      shiftPressed ? ui.KeyEventType.down : ui.KeyEventType.up,
      eventTimestamp,
    );
  }

  void _synthesizeModifierIfNeeded(
    int physicalLeft,
    int physicalRight,
    int logicalLeft,
    ui.KeyEventType type,
    num domTimestamp,
  ) {
    final bool leftPressed = _pressingRecords.containsKey(physicalLeft);
    final bool rightPressed = _pressingRecords.containsKey(physicalRight);
    final bool alreadyPressed = leftPressed || rightPressed;
    final bool synthesizeDown = type == ui.KeyEventType.down && !alreadyPressed;
    final bool synthesizeUp = type == ui.KeyEventType.up && alreadyPressed;

    // Synthesize a down event only for the left key if right and left are not pressed
    if (synthesizeDown) {
      _synthesizeKeyDownEvent(domTimestamp, physicalLeft, logicalLeft);
    }

    // Synthesize an up event for left key if pressed
    if (synthesizeUp && leftPressed) {
      final int knownLogicalKey = _pressingRecords[physicalLeft]!;
      _synthesizeKeyUpEvent(domTimestamp, physicalLeft, knownLogicalKey);
    }

    // Synthesize an up event for right key if pressed
    if (synthesizeUp && rightPressed) {
      final int knownLogicalKey = _pressingRecords[physicalRight]!;
      _synthesizeKeyUpEvent(domTimestamp, physicalRight, knownLogicalKey);
    }
  }

  void _synthesizeKeyDownEvent(num domTimestamp, int physical, int logical) {
    performDispatchKeyData(
      ui.KeyData(
        timeStamp: _eventTimeStampToDuration(domTimestamp),
        type: ui.KeyEventType.down,
        physical: physical,
        logical: logical,
        character: null,
        synthesized: true,
      ),
    );
    // Update pressing state
    _pressingRecords[physical] = logical;
  }

  void _synthesizeKeyUpEvent(num domTimestamp, int physical, int logical) {
    performDispatchKeyData(
      ui.KeyData(
        timeStamp: _eventTimeStampToDuration(domTimestamp),
        type: ui.KeyEventType.up,
        physical: physical,
        logical: logical,
        character: null,
        synthesized: true,
      ),
    );
    // Update pressing states
    _pressingRecords.remove(physical);
  }

  bool keyIsPressed(int physical) {
    return _pressingRecords.containsKey(physical);
  }

  void clearPressedKeys() {
    _pressingRecords.clear();
  }
}
